Gyromagnetic isolator with low reluctance material within single ridge and fluid coolant adjacent waveguide



1965 E. WANTUCH 3,212,028

GYROMAGNETIC ISOLATOR WITH LOW RELUCTANCE MATERIAL WITHIN SINGLE RIDGEAND FLUID COOLANT ADJACENT WAVEGUIDE Filed March 19, 1962 F .5 Erner/WWW/1 W fl K [62% ,l/farney United States Patent GYROMAGNETIC ISOLATORWITH LOW RELUC- TANCE MATERIAL WITHIN SINGLE RIDGE AND FLUID COULAN'IADJACENT WAVE- GUIDE Ernest Wantuch, Livingston, N..I., assiguor toAirtron, Inc., Morris Plains, NJ. Filed Mar. 19, 1962, Ser. No. 180,6767 (Ilaims. (Cl. 333-242) This invention relates to microwave isolators,and more particularly to ridge waveguide isolators.

In microwave systems, it is frequently necessary to isolate onecomponent from another. Nonreciprocal de vices using ferrite or othergyromagnetic material have been employed for these purposes. However, inthe case of broadband, high power, isolator requirements, no altogethersatisfactory solutions are available. Thus, in the case of one systememploying three-inch diameter coaxial lines, it had been proposed toemploy a reduced height fundamental mode waveguide isolator incombination with a pair of coaxial transitions. However, the fundamentalmode waveguide was 21 inches wide, requiring more space than wasavailable in the system in question. It has also previously beenproposed to use dual ridge waveguides for low power isolators, in viewof their relatively small size. In such arrangements, however, theferrite is supported by means of dielectric material and thus cannotreadily be cooled; this dual ridge structure is therefore not practicalfor high power requirements.

Accordingly, principal objects of the present invention are to increasethe power-handling capabilities and to reduce the size of microwaveisolator structures.

A collateral object of the present invention is to provide such anisolator for insertion in a coaxial waveguide system.

In accordance with the present invention, the foregoing objects areachieved through the use of a single ridge Waveguide with ferrite orother gyromagnetic material located on the broad flat sidewall of theridge waveguide, preferably opposite the edge or edges of the ridge. Amagnet may have its two poles in contact with the outer surface of thewaveguide on its broad flat sidewall, on either side of the centerlineof the waveguide, opposite the ferrite material. To close the magneticcircuit, a polepiece is provided within the waveguide ridge.

The resultant structure is eminently suitable for the intended purposeas the radio frequency signals are circularly polarized in the vicinityof the edges of the single ridge waveguide and the circular polarizationis opposite at the two edges. Similarly, the direction of magnetizationis opposite in the ferrite material adjacent the two edges of the ridgewaveguide, as the magnetic field comes down through one of the ferritesand up through the other element of ferrite.

The cooling problem is also solved, as the ferrites are inheat-conducting contact with the conductive metal wall of the waveguide.In addition to the cooling effect provided by the conductive waveguidewall itself, supplemental cooling structures, such as heat radiatingfins or a water-cooling system, may be provided. In these cases, ofcourse, the high conductivity of the waveguide structure permits therapid transfer of heat from the ferrites to the external coolingarrangements.

For insertion in a coaxial waveguide, the ridge waveguide wasdimensioned to present the characteristic impedance of the coaxial line.Under these circumstances, a simple door knob type transition in whichthe coaxial line was rigidly mounted to the top of the Waveguide ridges,was employed. This transition had a voltage standing wave ratio of lessthan 1.12 over a 50 megacycle bandwidth in the 400 megacycle frequencyrange.

3,212,028 Patented Oct. 12, 1965 lCe Advantages of the present unitinclude its relatively small size and weight, in addition to its highpower handling capabilities. One representative unit embodying theprinciples of the invention was approximately onehalf the size andweight of previous units.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of construction,together with further objects, features and advantages thereof, will bebetter understood from a consideration of the following description andthe accompanying drawings in which illustrative embodiments of theinvention are disclosed, by way of example. It is to be expresslyunderstood, however, that the drawings are for the purposes ofillustration and description only, and do not constitute a limitation ofthe invention.

In the drawings:

FIG. 1 is an overall view of an isolator of the present invention;

FIG. 2 is a cross-sectional view taken along lines AA of FIG. 1; and

FIG. 3 is a partial cross-sectional view through one of the coaxialtransitions of the isolator of FIG. 1.

Referring to the drawings, FIG. 1 is an assembly view of the ridgewaveguide of the present invention. In FIG. 1, the single ridgewaveguide 12 has its ridge in its lower surface, which is not visible inthis view. The two circular stubs 14 and 16 which extends upward fromthe ends of the ridge waveguide assembly 12 are connectors for securingthe isolator to coaxial lines. The upper surface of the ridge waveguidestructure 12 carries a set of three permanent magnets 18, 2t) and 22 forbiasing the ferrite strips which perform the isolation function withinthe ridge waveguide. The ferrite elements are not visible in FIG. 1, asthey are mounted inside and against the upper broad sidewall of thesingle ridge waveguide 12.

The cooling system for dissipating heat absorbed by the ferrite elementsincludes the two end manifolds 241 and 26 and the four coolant channels28 which extend between the manifolds 2d and 26. Suitable fittings 3t)and 32 are provided for directing water or other suitable coolantthrough the coolant system.

The cross-sectional view of FIG. 2 is taken along lines AA of FIG. 1.Clearly visible in the showing of FIG. 2 are the ferrite elements 42 and44. They are located adjacent the edges of the waveguide ridge structure46. The waveguide ridge, like the remainder of the conductively-boundedwave-guide channel 12, may be made of conductive material such asaluminum. Within the ridge structure 46 is a plate 48 of magneticmaterial. The member 48 closes the magnetic path from one pole of thepermanent magnet 13 to the other pole. This magnetic circuit serves tobias the ferrite elements 42 and 44 with steady magnetic fields whichare directed, respectively, upward and downward, as indicated by thearrows.

The general theory of isolator action is well known and is disclosed,for example, in S. E. Miller Patent No. 2,946,025, granted luly 19,1960. In brief, the theory involves the selective attenuation ofelectromagnetic field energy which is circularly polarized bygyromagnetic material biased by steady magnetic field which is properlyoriented with respect to the circularly polarized radio frequencymagnetic field. In the present case, the circularly polarized radiofrequency magnetic fields are polarized in predetermined senses for onedirection of transmission through the single ridge waveguide 12 and arepolarized in the opposite senses for transmission in the oppositedirection through the ridge waveguide 12. The electromagnetic waves aretherefore coupled to the magnetically biased ferrite elements 42 and 44for one direction of transmission but not for the opposite direction oftransmission. The coupling of the electromagnetic waves to the ferritematerial produces loss and heating of the ferrite. Accordingly, energyis freely transmitted through the ridge waveguide isolator in onedirection but little or no energy is transmitted through the isolatorstructure in the opposite direction.

The heat generated in the ferrite material is conducted by the metal ofthe broad wall 52 of the waveguide 12 to the coolant channels 28 fromwhich the heat is dissipated. The Walls of the coolant channels 28should, of course, be made of some relatively high heat conductionmaterial such as aluminum or copper.

FIG. 3 is a partial cross-sectional view taken through the center of theleft-hand end of the assembly of FIG. 1. In this figure, the coaxialconnection stub 14 is clearly shown and the nature of the simple doorknob type of transition is also disclosed. The transition includes anouter center conductor element 54, an enlarged circular element 56, anda tapered conical portion 58 which interconnects elements 54 and 56.This door knob type transition is secured to the ridge 46 of the singleridge waveguide 12. The showing of FIG. 3 does not include the magnetsor cooling structure, for purposes of simplicity. In addition, FIG. 3terminates with the flange 60 and does not show the second coaxial stub16 of FIG. 1.

In one particular embodiment of the invention, the single ridgewaveguide was designed to cover the frequency range from 400 to 450megacycles per second. The coaxial lines were 3% inches in diameter. Theembodiment of the present invention had a voltage standing wave ratio ofless than 1.12 over this frequency band. Nickel aluminate ferrite stripshaving an overall length of 18 inches provided a minimum of six decibelsisolation in the single ridge waveguide arrangement. The permanentmagnets bias the ferrite elements to resonance. The isolator hassuccessfully handled three megawatt peak and five kilowatt averagepowers with a coolant temperature of 50 C. The insertion loss, measuredunder high power conditions, was 0.3 decibel, yielding a front-tobackratio of 20 to 1. The overall length of the isolator, including bothinput and output transitions to the coaxial line, is about 42 inches andthe device weighs approximately 100 pounds. The unit is made airtight towithstand a pressurization of more than two atmospheres. As noted above,the illustrative embodiment of the invention is approximately one-halfthe size and Weight of previous designs.

It is to be understood that the above-described arrangements areillustrative of the applications of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention. Thus, byway of example and not of limitation, the ferrite strips may be replacedwith other gyromagnetic materials, and the isolator may be used insystems which are not coaxial. Similarly, with regard to coolingarrangements, the waveguide itself provides considerable cooling eifect,and radiating fins may be used instead of liquid cooling when theyprovide sutficient cooling action. Accordingly, from the foregoingremarks, it is to be understood that the preceding description shall beinterpreted as illustrative of the invention, and that the appendedclaims shall be accorded as broad an interpretation as is consistentwith the concepts herein taught.

What is claimed is:

1. A compact high power microwave isolator comprising:

a single ridge waveguide;

first and second strips of gyromagnetic material mounted opposite theedges of the ridge on the broad flat inner wall of the waveguide;

a magnet mounted outside the Waveguide with its first and second polesmounted against the broad fiat wall of the waveguide opposite said firstand second gyromagnetic strips;

a polepiece mounted within the ridge of the single ridge waveguide toclose the magnetic path through the two gyromagnetic elements; and

means for dissipating heat in contact with the broad wall of saidwaveguide.

2. A compact high power microwave isolator comprising:

a single ridge waveguide;

first and second gyromagnetic elements mounted opposite the edges of theridge on the broad flat wall of the waveguide;

a permanent magnet mounted outside the waveguide with its first andsecond poles mounted against the broad fiat wall of the Waveguideopposite said first and second gyromagnetic elements;

a polepiece mounted within the ridge to close the magnetic path throughthe two gyromagnetic elements; and

a cooling system in contact with said Waveguide.

3. A compact high power microwave isolator comprising:

a single ridge waveguide;

first and second gyromagnetic elements mounted opposite the edges of theridge on the broad flat wall of the Waveguide;

a magnet mounted outside the waveguide with its first and second polesmounted against the broad fiat wall of the waveguide opposite said firstand second gyromagnetic elements; and

a polepiece mounted within the ridge to close the magnetic path throughthe two gyromagnetic elements.

4. A compact high power microwave isolator comprising:

a single ridge waveguide;

gyromagnetic material mounted in heat transferring contact with thebroad fiat wall of the waveguide;

a magnet mounted outside the waveguide with its first and second polesmounted against the broad flat wall of the waveguide opposite saidgyromagnetic material; and

a polepiece mounted within the ridge to close the mag netic path throughthe gyromagnetic material.

5. A high power compact isolator for insertion in a coaxial line,comprising:

coaxial input and output connectors;

a section of single ridge waveguide;

transition elements mounted on the upper surface of both ends of theridge and connected respectively to the coaxial connectors, saidtransition elements being enlarged adjacent the ridge, and decreasing incrosssection near said connections;

gyromagnetic material mounted off center on the broad wall within thesingle ridge waveguide near the edges of the ridge; and

means for applying a steady biasing magnetic field to the gyromagneticmaterial.

6. A high power compact isolator for insertion in a coaxial line,comprising:

coaxial input and output connectors;

21 section of single ridge waveguide;

transition elements mounted on the upper surface of both ends of theridge and connected respectively to the coaxial connectors, saidtransition elements being enlarged adjacent the ridge, and decreasing incrosssection near said connections;

gyromagnetic material mounted off center on the broad wall within thesingle ridge waveguide near the edges of the ridge;

means for applying a steady biasing magnetic field to the gyromagneticmaterial; and

cooling means in contact with the outer surface of the broad wall of thewaveguide.

7. A compact high power microwave isolator for insertion in a coaxialline comprising:

a section of single ridge waveguide;

first and second gyromagnetic strips mounted opposite the edges of theridge 0n the broad flat inner wall of the waveguide;

a magnet mounted outside the waveguide with its first and second polesmounted against the broad flat wall of the waveguide opposite said firstand second gyromagnetic strips;

a polepiece mounted within the ridge of the single ridge waveguide toclose the magnetic path through the two gyrornagnetic elements;

means for dissipating heat in contact with the broad wall of saidWaveguide;

coaxial input and output connectors; and

transition means mounted on the upper surface of both ends of the ridgeand connected respectively to the coaxial connectors.

References tCited by the Examiner UNITED STATES PATENTS OTHER REFERENCESSouthworth: Waveguide Transmission, Van Nostrand Co., pages 134136relied upon, 1950.

ELI LIEBERMAN, Primary Examiner.

15 HERMAN KARL SAALBACH, Examiner.

1. A COMPACT HIGH POWER MICROWAVE ISOLATOR COMPRISING: A SINGLE RIDGEWAVEGUIDE; FIRST AND SECOND STRIPS OF GYROMAGNETIC MATERIAL MOUNTEDOPPOSITE THE EDGES OF THE RIDGE ON THE BOARD FLAT INNER WALL OF THEWAVEGUIDE; A MAGNET MOUNTED OUTSIDE THE WAVEGUIDE WITH ITS FIRST ANDSECOND POLES MOUNTED AGAINST THE BROAD FLAT WALL OF THE WAVEGUIDEOPPOSITE SAID FIRST AND SECOND GYROMAGNETIC STRIPS;